Investigation of Local Hydration Structures of Alkanethiol Self-Assembled Monolayers with Different Molecular Structures by FM-AFM

Hydration structures play crucial roles in a wide variety of chemical and biological phenomena. However, the key factors that determine the hydration structure remain an open question. Most recent studies have focused on the electrostatic interactions between the surface charges and dipoles of the water molecules, which are determined by the atomic/ionic species of the outermost solid surface, as the dominating factor. The number of studies on the correlation between the hydration structure and the atomic-scale surface corrugation has been limited. In this study, we investigated the hydration structures of alkanethiol self-assembled monolayers terminated with a hydroxyl group using frequency-modulated atomic force microscopy. We observed two molecular structures, namely, the (√3x√3)R30° structure and the c(4x2) superlattice structure, and found that their hydration structures are different mainly due to the slight differences in their molecular arrangements. This result suggests that a slight difference i...